In one aspect, the present inventions relate to methods and circuitry to adaptively charge a battery/cell using the state of health thereof. The state of health (SOH) of a battery (for example, a rechargeable lithium-ion (Li+) battery, is a parameter that describes, characterizes and/or is representative of the “age” of the battery cell and/or ability of the battery cell to hold charge, for example, relative to a given time in operation (for example, the initial time in operation). The SOH of a battery provides information to estimate, calculate, measure and/or determine other battery parameters, for example state of charge (SOC) and the voltage of the battery. Indeed, the voltage at the terminals of the battery changes as the SOH changes—and, hence the voltage curves of the battery shift as it ages and its SOH deteriorates.
Briefly, in a lithium-ion battery, a typical degradation process is the formation and thickening of layers around the electrodes that impede the transport of the lithium ions, one prominent example is the SEI layer around the anode. In other types of batteries, materials and chemistries, the transport of carriers across the battery cell is also impeded as the cell degrades, often as a result of worsening diffusion dynamics. Therefore, it is advantageous to monitor the degree that the flow of charge carriers is impeded, and use it as an estimation of the SOH of the battery. Indeed, estimating, calculating, measuring and/or determining the SOH of a battery may be useful in accurately estimating, calculating, measuring and/or determining the SOC of the battery.
In one embodiment, the adaptive charging techniques and/or circuitry uses and/or employs SOH and/or SOC data, in connection with certain constraints or requirements (that will be described below) to change, adjust, control and/or vary the charging current signal(s), including the characteristics thereof (including, for example, shape of charge and/or discharge signal (if any), amplitude thereof, duration thereof, duty cycle thereof and/or rest period (if any)), applied to the terminals of the battery/cell.
Notably, two considerations in connection with implementing adaptive charging circuitry and techniques may include (i) minimizing and/or reducing total charging time and (ii) maximizing and/or increasing cycle life. In this regard, for practical reasons, the battery/cell is charged within a given period of time (for example, a maximum allowed period of time). Typically, a specification value is defined or chosen depending on the application. For example, it is approximately two to four hours for batteries employed in consumer applications, and for batteries employed in transportation applications, it may be up to 8 hours. This results in a specification for a net effective average charging current over the duration of the charging period.
In addition, to maximizing and/or increasing cycle life of the battery/cell, it may be desirable to charge the battery/cell (i) at a lower current and/or (ii) provide rest periods between or in periods of charging (for example, between charging signals or packets) wherein no charge is applied to or injected into the battery/cell. Thus, in certain aspects, the charging circuitry of the present inventions implement adaptive techniques which seek to (i) minimize and/or reduce total charging time of the battery/cell and (ii) maximize and/or increase the cycle life of the battery/cell (by, for example, minimizing and/or reducing degradation mechanisms of the charging operation).
Additionally, estimating, calculating, measuring and/or determining the SOH of a battery may be useful in adaptively charging battery cell to accommodate or account for SOH, and/or changes therein, of the battery. An adaptive charging algorithm may employ the SOH to adjust, modify and/or change a charging current profile accordingly.
The present inventions also relate to techniques or methods of estimating, measuring, calculating, assessing and/or determining characteristics or parameters of the battery/cell including, for example, a terminal voltage (and/or changes therein) of a battery/cell, state of charge (and/or changes therein) of a battery/cell, and/or a relaxation time (and/or changes therein) of a battery/cell, a state of health (and/or changes therein) of a battery/cell. Notably, data which is representative of characteristics or parameters of the battery/cell (for example, the state of charge, relaxation time, impedance, state of health and/or terminal voltage) may be dependent on temperature. With that in mind in the discussion below, in connection with circuitry and techniques for adaptively charging a battery, it will be implicit that there may be a dependence on temperature. As such, while temperature may not be necessarily mentioned below, such data may be dependent on the temperature of the battery